Zero-heat-flux, deep tissue temperature measurement system
A zero-heat-flux, deep tissue temperature measurement system measures internal body temperature by way of a probe having a heater and thermal sensors arranged in a zero-heat-flux construction. The measurement system includes control mechanization that determines heater and skin temperatures based upon data obtained from the probe and uses those temperatures to calculate a deep tissue temperature. The measurement system includes a signal interface cable having a connector where a probe can be releasably connected to the system. The cable and attached connector are a removable and replaceable part of the system, separate from the probe. The measurement system provides an output signal imitating a standard input signal configuration used by other equipment.
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The subject matter relates to a system for measurement of deep tissue temperature (DTT) as an indication of the core body temperature of humans or animals. More particularly, the subject matter relates to constructions and operations of a zero-heat-flux DTT measurement system with a cable interface for connection to a disposable DTT probe.
Deep tissue temperature is a proxy measure for core temperature, which is the mass-weighted mean temperature of the body contents. It is desirable to maintain core body temperature in a normothermic range in many clinical situations. For example, during the perioperative cycle maintenance of normothermia has been shown to reduce the incidence of many adverse consequences of anesthesia and surgery, including surgical site infections and bleeding; accordingly, it is beneficial to monitor a patient's body core temperature before, during, and after surgery. Of course noninvasive measurement is highly desirable, for the safety and the comfort of a patient, and for the convenience of the clinician. Thus, it is most advantageous to obtain a noninvasive DTT measurement by way of a device placed on the skin.
Noninvasive measurement of DTT by means of a zero-heat-flux device was described by Fox and Solman in 1971 (Fox R H, Solman A J. A new technique for monitoring the deep body temperature in man from the intact skin surface. J. Physiol. Jan 1971:212(2): pp 8-10). Because the measurement depends on the absence of heat flux through the skin area where measurement takes place, the technique is referred to as a “zero-heat-flux” (ZHF) temperature measurement. The Fox/Solman system, illustrated in
The Fox/Solman and Togawa devices utilize heat flux normal to the body to control the operation of a heater that blocks heat flow from the skin through a thermal resistance in order to achieve a desired zero heat flux condition. This results in a construction that stacks the heater, thermal resistance, and thermal sensors of a ZHF temperature measurement device, which can result in a substantial vertical profile. The thermal mass added by Togawa's cover improves the stability of the Fox/Solman design and makes the measurement of deep tissue temperature more accurate. In this regard, since the goal is to achieve zero heat flux through the device, the more thermal resistance the better. However, the additional thermal resistance adds mass and size, and also increases the time required to reach a stable temperature.
The size, mass, and cost of the Fox/Solman and Togawa devices do not promote disposability. Consequently, they must be sanitized after use, which exposes them to wear and tear and undetectable damage. The devices must also be stored for reuse. As a result, use of these devices raises the costs associated with zero-heat-flux DTT measurement and can pose a significant risk of cross contamination between patients. It is thus desirable to reduce the size and mass of a zero-heat-flux DTT measurement device, without compromising its performance, in order to promote disposability.
Inexpensive, disposable, zero-heat-flux DTT measurement devices are described and illustrated in the related US patent applications (“the related applications”). A measurement device constructed according to the related applications is attached to the skin of a human or animal subject to sense the temperature of tissue deep under the skin. The measurement device is constituted of a flexible substrate and an electrical circuit disposed on a surface of the flexible substrate. The electrical circuit includes an essentially planar heater which is defined by an electrically conductive copper trace and which surrounds an unheated zone of the surface, a first thermal sensor disposed in the zone, a second thermal sensor disposed outside of the heater trace, a plurality of contact pads disposed outside of the heater trace, and a plurality of conductive traces that connect the first and second thermal sensors and the heater trace with the plurality of contact pads. Sections of the flexible substrate are folded together to place the first and second thermal sensors in proximity to each other. A layer of insulation disposed between the sections separates the first and second thermal sensors. The measurement device is oriented for operation so as to position the heater and the first thermal sensor on one side of the layer of insulation and the second thermal sensor on the other and in close proximity to an area of skin where a measurement is to be taken. The layout of the electrical circuit on a surface of the flexible substrate provides a low-profile, zero-heat-flux DTT measurement device that is essentially planar, even when the sections are folded together. Such devices are referred to as “sensors” or “probes”. In the following specification such a device will be referred to as a “probe” in order to avoid ambiguity with respect to the term “thermal sensor”, which is used in the specification to denote a device having an electrical property that changes in response to a change in temperature.
Given the advances in construction and performance of lightweight, disposable probes as is evidenced in the related applications, it is now desirable to establish system mechanizations and procedures that quickly produce accurate and reliable temperature measurements in response to sensed data produced by such probes. In particular, there is a need for a zero-heat-flux deep tissue temperature (DTT) measurement system that measures internal body temperature by way of a lightweight, disposable measurement probe that includes a heater and thermal sensors disposed in a zero-heat-flux construction.
Further, such a measurement system can have a construction customized for stand-alone operation. That is to say, one that does not include a standard signal output that can be accepted as an input by multi-function patient monitors. However, it is desirable that such an output signal interface conforming to a standard device or a standard input signal configuration defined for multi-function patient monitors would increase the versatility and usefulness of such a zero-heat-flux DTT measurement system.
SUMMARYIn one aspect, the disclosure concerns a zero-heat-flux DTT measurement system with a simple, low cost interface suitable for being used with disposable probes.
In another aspect, the disclosure concerns simple, effective, and inexpensive system control mechanization for lightweight probes with low thermal mass.
In yet another aspect, the disclosure concerns a zero-heat-flux DTT measurement system with a simple, low cost output signal interface conforming to a standard input signal configuration for multi-function patient monitors.
These and other aspects are embodied in a zero-heat-flux DTT measurement system with a signal interface where a probe can be connected to and disconnected from the system.
Preferably, a programmable memory for storing system information including thermal sensor calibration coefficients is located on the probe together with a heater and thermal sensors.
These and other aspects are embodied in a zero-heat-flux, DTT measurement system implementing control mechanization that checks signal continuity between the system and a probe, validates probe operation, determines skin and heater temperatures, and executes a control loop with safety measures related to measured skin and heater temperatures.
These and other aspects are embodied in a zero-heat-flux, DTT measurement system including an output signal interface conforming to a standard input signal configuration for multi-function patient monitor.
These and other aspects are embodied in a method of operating a zero-heat-flux, DTT measurement probe with a heater and thermistors for sensing skin and heater temperatures, by checking signal continuity between the probe and a probe control mechanization, validating operation of the thermal sensors, determining skin and heater temperatures sensed by the thermistors, executing a control loop to operate the heater with safety measures that are related to the measured skin and heater temperatures.
These and other aspects are embodied in a method of operating a zero-heat-flux, DTT measurement probe with a heater, thermistors, and a programmable memory device, by executing a control loop to operate the probe with security measures that are related to integrity of data and probe use information associated with the probe.
In another aspect, the disclosure concerns a signal interface conforming to a standard device or a standard input signal configuration.
This and other aspects are embodied in a system and method for emulating a standard thermistor output signal indicative of deep tissue temperature.
A zero-heat-flux deep tissue temperature (DTT) measurement system measures internal body temperature by way of a zero-heat-flux DTT measurement probe that includes a heater and thermal sensors in a zero-heat-flux construction. The measurement system includes a processing and display unit with control mechanization that checks signal continuity with the probe, authenticates probe identity, decrements a use count of the probe, determines heater and skin temperatures based upon information obtained from the probe, and calculates a deep tissue temperature. The control loop implements safety measures related to measured temperatures and security measures related to integrity of data and probe use information associated with the probe. The measurement system includes a signal interface cable with an attached connector by which a probe can be physically, releasably, and electrically coupled to the system. The cable and connector together constitute a single element that is a removable and replaceable part of the system, separate from the probe. A standard output signal indicative of deep tissue temperature is provided by a measurement system emulation unit that imitates operation of a thermal sensor device.
A zero-heat-flux DTT measurement probe (hereinafter, simply “a probe”) includes at least two thermal sensors, a heater, and a programmable memory device. For example, a construction for such a probe includes a flexible substrate with at least two thermal sensors disposed thereon in a spaced-apart relationship. Preferably the thermal sensors are maintained in a spaced apart relationship on respective substrate layers by a flexible thermal insulator positioned between the layers. The substrate supports at least the thermal sensors, the separating thermal insulator, the programmable memory device, and the heater. The probe construction includes a periphery with a tab by which the probe is removeably coupled with a probe signal interface cable connector.
Although a particular zero-heat-flux DTT measurement system is described in terms of a preferred embodiment comprising representative elements, the embodiment is merely illustrative. It is possible that other embodiments will include more elements, or fewer, than described. It is also possible that some of the described elements will be deleted, and/or other elements that are not described will be added. Further, elements may be combined with other elements, and/or partitioned into additional elements.
Zero-Heat-Flux DTT Measurement System
As per
As seen in
Zero-Heat-Flux DTT Probe Construction
Zero-heat-flux DTT measurement probes that can be used in the zero-heat-flux DTT measurement system are preferably, but not necessarily, constructed according to the related applications. An example of a disposable probe representative of the probe 44 in
As seen in
With reference to
With reference to
As per
As seen in
Preferably, but not necessarily, the heater 126 has a non-uniform power density construction that can be understood with reference to
The differing power densities of the heater portions 128 and 129 may be invariant within each portion; alternatively, they may vary. Variation of power density may be step-wise or continuous. Power density is most simply and economically established by the width of the heater trace 124 and/or the pitch (distance) between the legs of a switchback pattern. For example, the resistance, and therefore the power generated by the heater trace, varies inversely with the width of the trace. For any resistance, the power generated by the heater trace also varies inversely with the pitch of (distance between) the switchback legs.
The electrical circuit 120 on the flexible substrate 101 seen in
Preferably, the programmable memory device 170 includes a multi-pin EEPROM mounted by mounting pads to the probe 44.
one lead of the second thermal sensor 142 (TH2) and pin 1 of the programmable memory device 170 are connected by conductive trace portions to contact pad 1;
leads of the first and second thermal sensors 140,142 and pin 4 of the programmable memory device 170 are connected by conductive trace portions to contact pad 2;
one lead of the first thermal sensor 140 (TH1) and pin 3 of the programmable memory device 170 are connected by conductive trace portions to contact pad 3;
pins 2 and 5 of the programmable memory device 170 are connected by a conductive trace portion to contact pad 4;
the return end of the heater trace 124 is connected by a conductive trace portion to contact pad 5; and
the input end of the heater trace 124 is connected by a conductive trace portion to contact pad 6.
With reference to
The probe 44, with the electrical circuit 120 laid out on one or more sides of the flexible substrate 101 as illustrated in
Probe Design Considerations
Design and manufacturing choices made with respect to a zero-heat-flux DTT measurement probe can influence its operation. One design choice relates to the thermal sensors used in the detection of the zero-heat-flux condition. Given the importance of core body temperature, it is very desirable that the thermal sensors produce accurate temperature data in order to enable reliable detection of the zero-heat-flux condition and accurate estimation of core body temperature. In this case, the tradeoff is between accuracy and cost of the thermal sensor. A number of thermal sensor devices can be used in zero-heat-flux DTT measurement. These devices include PN junctions, resistive temperature devices, and thermistors, for example. Thermistors are a preferred choice for reasons of small size, handling convenience, ease of use, and reliability in the temperature range of interest. Their relatively low cost makes them desirable candidates for single-use, disposable probes.
The magnitude of a thermistor's resistance changes in response to a change of the temperature of the thermistor. Thus, to determine the magnitude of the temperature, the thermistor's resistance is measured and converted to a temperature value using a known relationship. However, batch-to-batch manufacturing differences can yield a large variance in thermistor resistance. For example, low-cost thermistors can exhibit a range of ±5% in resistance values from device to device at a given temperature, which yields a range of ±2.5° C. in reported temperature. A variance can compromise the accuracy and reliability of zero-heat-flux temperature measurement. Thus, while it is desirable to use such thermistors in order to limit the cost of parts and labor in manufacturing zero-heat-flux DTT probes, it is important to correct for the effects of resistance variance on device operation.
The range of thermistor resistance variance can be corrected by calibration of thermistor resistance using known methods, such as the Steinhart-Hart equation, which require knowledge of coefficients derived from values of thermistor resistance measured at fixed temperatures. When a thermistor is operated in its temperature measuring mode, the coefficients are used in known formulas to correct or adjust the magnitude of its indicated temperature. Such correction is called calibration.
System/Probe Signal Interface
The physical layout shown in
Presuming that the programmable memory device 170 includes an EEPROM, a separate signal path is provided for EEPROM ground, and the thermal sensor signal paths are shared with various pins of the EEPROM as per
With reference to
The probe can be fabricated using the materials and parts listed in the following table. An electrical circuit with copper traces and pads is formed on a flexible substrate of polyester film by a conventional photo-etching technique and thermal sensors are mounted using a conventional surface mount technique. The dimensions in the table are thicknesses, except that Ø signifies diameter. Of course, these materials and dimensions are only illustrative and in no way limit the scope of this specification. For example, the traces may be made wholly or partly with electrically conductive ink. In another example, the thermal sensors are preferably thermistors, but PN junctions or resistance temperature detectors can also be used.
Zero-Heat-Flux DTT Measurement System Control Mechanization
With reference to
As per
With further reference to
With further reference to
With further reference to
With reference to
The YSI-400 thermistor signal is accepted as input by many patient monitors. The measurement system 40 emulates this output signal by driving the EMU 227 to provide a resistance value from the YSI-400 calibration chart equivalent to the DTT temperature. In this fashion, any monitor that accepts YSI-400 output will also accept output from the measurement system 40.
With reference to
In operation, the LED 228 converts the skin temperature value to light of an intensity that causes the resistance of the output photocell 229 to equal the resistance of a YSI-400 thermistor held at the same temperature. Light from the LED 228 also impinges on the reference photocell 230. The EMU 227 controls the intensity of the LED 228 based on resistance of the reference photocell 230 to correct for small variations in LED output and photocell sensitivity. The emulation logic 211 exercises control over the EMU 227 by way of a digital-to-analog converter (DAC) 231 and an analog-to-digital (A/D) converter 232 (ADC). Based on the current value of Ts, which is stored in digital form by the controller 200, the emulation logic 211 generates an LED drive signal. The drive signal has a magnitude that causes the LED 228 to emit light of such intensity as will cause the output photocell 229 to assume the resistance value that would be produced by the emulated thermistor in response to Ts. The drive signal is converted from digital to analog form by DAC 231; a voltage-to-current converter 233 generates a current from the analog voltage produced by the DAC 231 that is applied to the LED 228. In order to confirm that the resistance value produced by the output photocell 229 is correct, the emulation logic 211 reads the resistance value of the reference photocell 230 via the ADC 232 and makes any necessary corrections by adjusting the LED drive signal. An EMU calibration circuit includes an output switch 234 that is controlled by the emulator logic 211 for the purpose of periodically rerouting the EMU output produced by the output photocell 229 to an ADC 235. This allows the initial calculation and periodic recheck of the conversion table (below).
The emulation logic 211 operates in response to a state flow that includes at least four states. In an OFF state, the switch 234 is operated to open the circuit to the patient monitor 56 so that the resistance is effectively infinite. In an ON state, the switch 234 closes the output circuit so that the patient monitor 56 can measure the resistance of the output photocell 229. In this state, the emulation logic 211 uses the values from the conversion table, below, to regulate the intensity of LED 228 with the aim of providing a desired output resistance value. In a COARSE CALIBRATION state, the switch 234 opens the circuit to the patient monitor 56 and closes the circuit to the ADC 235. The emulation logic 211 then constructs a coarse approximation of a conversion table. In a FINE CALIBRATION state, the switch 234 opens the circuit to the patient monitor 56 and closes the circuit to the ADC 235. The emulation logic 211 then corrects the conversion table for any errors that may have occurred since the coarse calibration was done.
The EMU 227 is operated by the emulation logic 211 with reference to a conversion table, an example of which is presented below. It is understood that the values in the table need not be perfect, but rather are held to within an acceptable degree of error. The first column of the conversion table represents DTT temperature at ZHF. The second column (YSI 400 Value) contains the target resistance value (in ohms) associated with the temperature in column 1. The third column (Emulation Photocell Output) provides an ADC setting taken from the photocell 229 during coarse calibration such that the resistance value of the emulation output photocell 229 taken at the EMU output jack 54 matches the YSI 400 value from column 2. The fourth column (Reference Photocell Output) provides an ADC setting taken from the reference photocell 230, which is associated with the Emulation Photocell Output setting in column 3.
In the ON state, the emulation logic 211 receives the current temperature value from within the MCU 202. Then the two temperature values in the table closest to the current temperature value are determined. The emulation logic then interpolates a target ADC value for the reference photocell 230. The DAC 231 is initially set to a mid-point setting after coarse calibration. DAC 231 drives the LED 228, which in turn illuminates both the output photocell 229 and the reference photocell 230. The output of the reference photocell 230 is then checked against the interpolated ADC target value via the ADC 235. If the value is different, the DAC 231 setting which drives the LED 228 is adjusted until the actual reference photocell output is the same as the interpolated target value. Once zeroed in, the DAC value continues to be updated so that the ADC 235 value tracks the target ADC value. This process is repeated on periodic basis to accommodate changes in the current temperature as well as changes in LED output and photocell response.
The COARSE CALIBRATION state occurs each time a probe is attached to a patient. First, the emulation logic 211 incrementally changes the illumination produced by the LED 228, running through a broad range of possible values. At regular intervals, the emulation logic 211 attempts to reach an LED power such that the resistance value of photocell 229 achieves the YSI 400 value associated with a target temperature (e.g., 25° C.). When this condition is achieved, the associated LED setting and reference photocell output are recorded in their respective columns in the conversion table. The logic 211 increments the LED and repeats the process until the conversion table is fully populated.
The FINE CALIBRATION state occurs periodically, with an interval chosen to be shorter than the time required for meaningful drift in the LED and photocell outputs. The emulator logic chooses the LED setting for a single target temperature based on the current temperature of the system. (e.g., 37.5° C.). Then, the resistance value of the reference photocell 230 is compared to the actual resistance value of output photocell 229. The difference is used to set a fixed offset that is used to compensate the reference photocell in order to eliminate the error on the output photocell.
The controller 200 can be assembled using parts listed in the following table. Of course, these parts are only illustrative and in no way limit the scope of this specification.
Zero-Heat-Flux DTT Measurement System Operation
The zero-heat-flux DTT measurement system 40 is constructed to measure deep tissue temperature in an orderly and directed manner in response to conditions it perceives and commands input to it by a system operator. The controller 200 of the system 40 governs the operations of the system 40 and the functions of the probe 44 connected to it, and processes data obtained from the probe in order to format it for control of the heater 126, for output (via the display panel 43 and the EMU 272), and for storage in the programmable storage device (hereinafter, the EEPROM) 170.
A method of deep tissue temperature measurement which is executed by the MCU 202 running the probe control logic 208 begins in
In the description to follow, parallel process streams are set forth with the understanding that the “process” being illustrated and described is a sequence of steps performed by the controller. Moreover, it is to be understood that the parallel operation of such streams is a convention understood by the person of ordinary skill in the art. The MCU 202 can run the various process streams sequentially, or in an interlaced fashion, but at such a speed that they appear parallel from the point of view of the system operator. These process streams are a probe disconnection sequence (stream F,
Further, all error conditions encountered in the operational sequences illustrated in
Referring now to
The following EEPROM memory map and pseudo-code sequence illustrate a routine executed by the controller for detecting connection of a DTT probe:
In the probe connection sequence, stream A of
Continuing the sequence of
Continuing the sequence of
Process stream D (
With process stream F (
With process stream H (
Refer now to
A family of curves representing the decaying offset term is illustrated in
With reference again to process stream H illustrated in
With process stream I (
If the criteria for equilibration are met, the controller, in step 337, causes the EMU system 227 to close the switch 234 to output signal jack 54 so as to provide the external patient monitor 56 with access to a resistance value equivalent to the patient temperature data. Then, in step 338, the controller initiates output of a steady screen (
At periodic intervals, for example, every five minutes, data are updated on the EEPROM 170. In step 341, the controller determines if the time interval has elapsed. If not, another set of data points is acquired (step 326). Otherwise, the running average of patient temperature is written to the EEPROM (step 332), with a write-error resulting in a probe error message (step 333). Next, the use time value on the EEPROM is updated, reflecting the time interval used in step 341. If the probe 44 has been plugged in for a time less than the time interval (i.e., the first time this step has occurred during the current use), the use count parameter read from the EEPROM is decremented by one (step 335) and the decremented use count is written to the EEPROM. As should be evident, the use count is decremented only once each time a probe is plugged in, and then only if a main data acquisition sequence has been initiated and the system has reached equilibrium (step 329) with no update error (step 340) and no trend write error (step 333). Stated another way, the use count is checked once (
If, in step 329, the controller determines that the probe 44 does not meet the criteria for equilibration, the EMU 227 is turned off (330), and, in step 331, the system remains in the EQUILIBRATION state 254 (
With process stream E (
In respect of step 348, with the preferred mode of heater control being pulse width modulation, a simple and effective heater safety circuit observes the heater operational parameters: a level of current through the heater, and a time that the heater remains on during any pulse of the PWM signal. A current level higher than a predetermined safety level (700 mA, for example) indicates a possible short circuit condition in the heater. A pulse width longer than a predetermined time (2 seconds, for example) indicates a possible fault that causes the heater switch 216 to stay on too long (which will overdrive the heater). A preferred heater safety circuit for a PWM heater control mode is illustrated in
Finally, in step 350, the controller applies criteria for detachment of the probe from a patient. In this regard, either: skin temperature falls below 30° C. and skin temperature is below heater temperature by a predetermined value (for example, 1.0° C.); or the slope of the skin temperature is <−625 m° C./5 seconds. If either condition is met, the controller, in step 351, returns the system to the READY state 252 (
With process stream G (
In some aspects, a calibration dongle is used to check the calibration of the zero-heat-flux DTT measurement system 40 (process stream B) and to initiate calibration of the emulation system (process stream G). In this regard, with process stream B (
In some aspects, a dongle is used to update programming of the zero-heat-flux DTT measurement system 40. Process stream C (
Typically less storage space is required for calibration than for programming, and so use of an 8-pin SOIC EEPROM permits both the calibration dongle and the programming dongle to share the same PCB. The wiring of the EEPROM, particularly with the WP (write protect) wired to the Vss (ground) in the circuit, allows both reading and writing to the EEPROM while attached to the dongle circuitry.
The calibration dongle preferably requires high precision (0.1%) resistors whose resistance matches closely with that of a 10KΩ thermistor near 36° C. The programming dongle only requires a low precision pull-up resistor whose resistance is 10 kΩ. The position of the resistors on the PCB allows the circuit to be visually identified. That is, if surface mounted resistors are placed in positions R1 and R3, the dongle can be identified programming dongle. A low precision 6.2Ω resistor can, optionally, populate position R5. This position allows the heater circuitry to be checked
Although principles of measurement system and probe construction and operation have been described with reference to presently preferred embodiments, it should be understood that various modifications can be made without departing from the spirit of the described principles. Accordingly, the principles are limited only by the following claims.
Claims
1. A temperature measurement system for measuring temperature, comprising:
- a probe comprising: a first substrate and a second substrate, the first and second substrates sandwiching a first thermally insulating material, a first thermal sensor disposed on the first substrate, and a second thermal sensor disposed on the second substrate;
- an information switch,
- a control unit configured to: receive first voltage signal from the first thermal sensor and a second voltage signal from the second thermal sensor; determine a first magnitude of resistance from the first voltage signal and a second magnitude of resistance from the second voltage signal; determine, using calibration information from a programmable memory device, a first temperature parameter from the first magnitude of resistance and a second temperature parameter from the second magnitude of resistance; determine a deep tissue temperature value based on a relationship between the first temperature parameter and the second temperature parameter; converting the deep tissue temperature value to a resistance signal that would be produced by a thermistor in response to the same temperature; and providing the resistance signal through an output jack; and
- wherein the control unit includes probe control logic, and wherein the information switch has a first state in which the information switch is operative to connect thermal sensor signals from the probe signal interface cable to the probe control logic and a second state in which the information switch is operative to connect programmable memory device information from the probe signal interface cable to the probe control logic.
2. The temperature measurement system of claim 1, wherein the programmable memory device stores calibration information of the first and second thermal sensors.
3. The temperature measurement system of claim 1, wherein the first state of the information switch blocks the transfer of programmable memory device signals from being transferred through the probe signal interface cable and the second state of the information switch enables the transfer of programmable memory device signals through the probe signal interface cable.
4. The temperature measurement system of claim 1, further comprising a layer of a second thermally insulating material attached to one side of the first substrate layer.
5. The temperature measurement system of claim 1, further comprising
- a heater switch;
- wherein the control unit is configured to: control the heater switch to bring the probe into a zero-heat flux condition; and
- wherein the probe comprises a heater.
6. The temperature measurement system of claim 5, further comprising:
- a probe signal interface cable configured to be electrically connected to the probe and the control unit; and
- wherein the heater switch is operative to switch a pulse-width-modulated drive signal through the probe signal interface cable to the heater.
7. The temperature measurement system of claim 5, wherein the control unit comprises probe control logic that calculates and reports the first temperature parameter based on analog-to-digital readings of the resistance of the first thermal sensor and the second thermal sensor.
8. The temperature measurement system of claim 6, wherein the probe control logic uses proportional-integral-derivative control to enable the heater to reach and maintain the zero-heat flux condition while in steady state.
9. The temperature measurement system of claim 1, wherein the output jack conforms to a common signal interface for electronic medical equipment.
10. The temperature measurement system of claim 1, wherein the control unit imitates the resistance of a YSI-400 thermistor.
11. A temperature measurement system, comprising:
- a measurement probe, a first thermal sensor operative to sense a first temperature, a second thermal sensor operative to sense a second temperature, and a connector;
- a processing unit comprising: a controller, a thermistor emulator, an emulator output jack, and an information switch,
- a probe signal interface cable configured to be electrically connected to the measurement probe and the processing unit;
- a programmable memory device;
- wherein the thermistor emulator operative to provide an emulator output signal at the emulator output jack; and
- wherein the information switch has a first state in which the information switch is operative to connect thermal sensor signals from the probe signal interface cable to the controller and a second state in which the information switch is operative to connect programmable memory device information from the probe signal interface cable to the controller and to connect information from the controller to the programmable memory device.
12. The temperature measurement system of claim 11, wherein the programmable memory device stores calibration information of the first and second thermal sensors.
13. The temperature measurement system of claim 11, in which the first state of the information switch blocks the transfer of programmable memory device signals from being transferred through the probe signal interface cable and the second state of the information switch enables the transfer of programmable memory device signals through the signal interface cable.
14. The temperature measurement system of claim 11, further comprising: an emulation output cable connected to the emulator output jack.
15. The temperature measurement system of claim 11, wherein the thermistor emulator emulates a YSI-400 thermistor.
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Type: Grant
Filed: Apr 28, 2016
Date of Patent: Apr 30, 2019
Patent Publication Number: 20160238463
Assignee: 3M INNOVATIVE PROPERTIES COMPANY (Saint Paul, MN)
Inventors: Mark T. Bieberich (Lakeway, TX), Philip G. Dion (St. Paul, MN), Gary L. Hansen (Inver Grove Heights, MN), David R. Palchak (San Francisco, CA), Timothy J. Prachar (Menlo Park, CA), Ryan J. Staab (Minneapolis, MN), Albert P. Van Duren (Stillwater, MN), Elecia White (Aptos, CA), Allen H. Ziaimehr (Arden Hills, MN)
Primary Examiner: Rene T Towa
Application Number: 15/140,694
International Classification: G01K 1/16 (20060101); G01K 7/22 (20060101); G01K 13/00 (20060101); G01K 15/00 (20060101);